1. Field of the Invention
The present invention relates to a wet-type electrophotographic image forming apparatus. More particularly, the present invention relates to an oxidation catalyst unit for judging a life span of an oxidation catalyst catalyzing an oxidation of carrier vapor generated when a printing sheet with a developer passes through a fixing unit, a wet-type electrophotographic image forming apparatus having the same, and a method for judging the life span of the oxidation catalyst.
2. Description of the Related Art
In general, wet-type electrophotographic image forming apparatuses such as laser beam printers irradiate a laser beam onto a photosensitive medium to form an electrostatic latent image, attach a developer to the electrostatic latent image to form a visible image, and transfer the visible image to a predetermined printing medium to output a desired image. Such a wet-type electrophotographic image forming apparatus can obtain a clearer image than a dry-type electrophotographic image forming apparatus using powdered toner and thus, is suitable for color printing.
FIG. 1 schematically illustrates the configuration of a conventional wet-type electrophotographic image forming apparatus.
As shown in FIG. 1, a conventional wet-type electrophotographic image forming apparatus comprises an image forming apparatus body 110, a plurality of photosensitive drums 121, 122, 123 and 124 (121 through 124), a plurality of charging units 131, 132, 133 and 134 (131 through 134), a plurality of exposing units 141, 142, 143 and 144 (141 through 144), a plurality of developing units 151, 152, 153 and 154 (151 through 154), a plurality of first transfer rollers 171, 172, 173 and 174 (171 through 174), a second transfer roller 180, and a fixing unit 190. Electrostatic latent images are formed on the plurality of photosensitive drums 121 through 124. The plurality of charging units 131 through 134 charge the plurality of photosensitive drums 121 through 124 with predetermined potentials, respectively. The plurality of exposing units 141 through 144 irradiate laser beams onto the charged photosensitive drums 121 through 124, respectively. The plurality of developing units 151 through 154 supply the photosensitive drums 121 through 124 with developer, respectively, to form visible images. The plurality of first transfer rollers 171 through 174 transfer the visible images from the photosensitive drums 121 through 124 to a transfer belt 160. The second transfer roller 180 transfers a final image formed on the transfer belt 160 through an overlap of the visible images to a printing sheet P. The fixing unit 190 applies heat and pressure to the printing sheet P to which the final image has been transferred to fuse and fix the final image on the printing sheet P.
The plurality of developing units 151 through 154 store developer of different colors and supply the plurality of photosensitive drums 121 through 124 with the developer of different colors, respectively. Here, the developer contains ink with dispersed toner and a liquid carrier such as Norpar. The Norpar carrier comprises a hydrocarbon-based solvent that is a compound of C10H22, C11H24, C12H26, and C13H28. The developer applied to the photosensitive drums 121 through 124 is transferred to the transfer belt 160 to form the visible images. The visible images are overlapped on the transfer belt 160 to form the final image, and then the final image is transferred to the printing sheet P. When the printing sheet P passes through the fixing unit 190, the ink of the developer is fused on the printing sheet P and the liquid carrier of the developer is changed into an inflammable hydrocarbon gas such as methane (CH4) by high heat and discharged to the outside.
The inflammable hydrocarbon gas is classified as a volatile organic compound (VOC). Thus, when the inflammable hydrocarbon gas is discharged, the inflammable hydrocarbon gas pollutes the surroundings and emits an unpleasant smell. To solve this problem, various methods of removing the resulting inflammable hydrocarbon gas are presented.
A conventional inflammable hydrocarbon gas removing method comprises a filtering method of physically removing a gas component using a carbon filter, such an activated carbon. Another conventional inflammable hydrocarbon gas removing method comprises a direct combustion method of burning a gas component at an ignition temperature between approximately 600° C. and 800° C. Still another conventional inflammable hydrocarbon gas removing method comprises an oxidation catalytic method of burning a gas component at a relatively low temperature between approximately 150° C. and 400° C. using a catalyst filter to oxidation-decompose the gas component into water and carbon dioxide.
In the filtering method, the carbon filter does not have an ability to decompose carrier collected therein. Thus, when the carbon filter is saturated with a predetermined amount or more of carrier, the carbon filter must be replaced with new one. In the direct combustion method, high heat is generated, which causes a safety problem.
To solve these problems, an oxidation catalytic method has recently been used as a method of removing carrier vapor of a wet-type electrophotographic image forming apparatus. Such an oxidation process is an exothermic reaction. Thus, when a catalyst filter normally reacts with carrier vapor, an atmospheric temperature of the catalyst filter after the reaction is higher than an atmospheric temperature of the catalyst filter before the reaction. However, in a case where the catalyst filter is exhausted due to heating or contamination and thus fails to normally react with the carrier vapor, the carrier vapor may not be normally decomposed and thus, may be discharged with a smell to the outside, which pollutes the surroundings.
Accordingly, a need exists for a system and method to easily and effectively determine a condition of a oxidation catalyst filter for use in a wet-type electrophotographic image forming apparatus.